Jerome,
I think I may know what is causing the problem.
When I opened one or more viewers on objects I had added / painted, the flap that was created to contain the viewers was bugging me so I alt-clicked it, and used the X-icon to delete it.
I see from looking at the debug/inspect owner chain that a viewer's owner/parent is normally the "viewer flap" (when the option "viewersInFlaps" is on.
I just tried to recreate deleting the viewer-flap before deleting the viewer(s), but when I do it now, the viewers are being deleted as well (as they should be, I assume). I'm almost sure I was somehow able to drag/move the viewer-flap at one point and the viewers were being "left behind". If I deleted the flap at that point I'm guessing the viewers would be "orphaned" and that might be what is causing the problem.
Mike
P.S. Can someone rename this thread to " .... *showFLAP*" instead of "FLAG" ... (stupid me) !